Net Loss Per Share - Reconciliation of Basic and Diluted Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (8,864)	$ (8,605)	$ (13,018)	$ (15,771)	$ (3,438)	$ (12,236)	$ (30,487)	$ (31,445)
Weighted average shares:
Basic shares (in shares)	37,436			36,904			37,382	37,410
Effect of dilutive securities—options and warrants outstanding (in shares)	0			0			0	0
Diluted shares (in shares)	37,436			36,904			37,382	37,410
Net income (loss) per share - basic (in dollars per share)	$ (0.24)			$ (0.43)			$ (0.82)	$ (0.84)
Net income (loss) per share - diluted (in dollars per share)	$ (0.24)			$ (0.43)			$ (0.82)	$ (0.84)